Synchronous generators have been used in hydropower from more than a century where, traditionally, the field current is transferred to the rotor using slip rings and carbon brushes. There are some major disadvantages following the use static excitation; regular and expensive maintenance, as well as a source of carbon dust which, due to buildup, may cause short circuits. To avoid these problems associated with slip ring exciter systems, a system that use induction to transfer power to the rotor could be used instead. Systems that utilize brushless excitation today usually regulates the current by controlling the magnetization of the exciter stator, which is comparably slower than their static counterparts. In order to allow for swift regulation of the field current from a brushless exciter, required power electronics and controllers have to be present on the rotor shaft instead. The aim of this project is to start investigating if commercially available products, which are originally indented to be used in a stationary environment, could accomplish this. The results from this study shows that it is possible to use such products to control the field current. The components were found to withstand the exposure of high g-forces and vibrations, albeit only during the relatively small amount of time in which rotary testing was performed. As such there is no certainty that the components would remain functional for the considerably longer time that any commercial use would require them to.

This diploma thesis is focused on the design of a rotating rectifier for a synchronous generator. Based on defined requirements, the new rotating rectifier concept has been created that allows a greater current range than existing rectifier used by Siemens Electric Machines s.r.o. The thesis is divided into five parts. The first part deals with the search of existing rotating rectifiers and other design possibilities. The requirements for the rotating rectifier were defined in the second part of the thesis. The following section deals with both electrical design of rectifier elements and varistors. The fourth part of the diploma thesis describes the thermal analysis. On the basis of thermal analysis the operating conditions of the rotating rectifier were determined. The last part of the thesis is devoted to mechanical and modal analysis. Based on these analyses, the strength and operability of the new rotating rectifier concept were verified.